1. Field of the Invention
The present invention relates to a foamed article. More specifically, the present invention relates to a foamed article which can be suitably used as, for instance, shoe soles and cushioning materials for automobiles and other vehicles, furniture and bedding, and the like.
Furthermore, the present invention relates to a process for preparing a polyurethane foam. More specifically, the present invention relates to a process for preparing a polyurethane foam, which can be suitably used as shoe soles, especially low-density soles, and the like.
2. Discussion of the Related Art
Foamed articles represented by polyurethane foams have been widely used in various fields. In general, properties required for foamed articles differ depending upon their purpose of use or sites used. From the viewpoints of safety, comfortable fitting and feel, there has been developed a polyurethane foam which has sufficient strength, soft and excellent feel, and low rebound resilience as the properties. However, there has not yet been produced a foamed article having sufficient strength, and simultaneously satisfying soft and excellent feel and low rebound resilience.
For instance, Japanese Patent Laid-Open No. 2002-47330 discloses a low-resilient polyurethane foam having excellent elongation and tensile strength. However, there are some defects in the polyurethane foam, such that the polyurethane foam has high storage modulus (E′) in dynamic viscoelasticity and does not have soft and excellent feel, nevertheless high strength and low resilience are satisfied.
In addition, Japanese Patent Laid Open No. Hei 11-286566 discloses a polyurethane foam having low resilience. However, there is a defect in this polyurethane foam, such that the polyurethane foam does not have sufficient hardness and strength at room temperature.
A polyether-based polyurethane has been used for shoe soles since the polyether-based polyurethane is excellent in hydrolytic resistance as compared to a polyester-based polyurethane.
However, there is a defect in the shoe sole made of the polyether-based polyurethane, such that the shoe sole has low mechanical strength when the shoe sole is made lighter in order that the shoes are fit more comfortably.
Japanese Patent Laid-Open No. Hei 3-121116 discloses a polyurethane composition for shoe soles, comprising a polyether-polyol, a chain extender, a blowing agent and an isocyanate or a terminal-diisocyanate prepolymer made of a compound having two active hydrogens and a diisocyanate, wherein the polyether-polyol has a molecular weight of 2000 to 10000. However, this document does not suggest a process for improving dimensional change with advancement of lighter weight at all.
Japanese Patent Laid-Open No. 2000-290345 discloses a process for preparing a polyurethane foam for shoe soles, comprising reacting a polyol composition comprising a polyol component comprising a polyoxypropylene glycol prepared from a compound having two hydroxyl groups as a starting material, and having a degree of unsaturation of at most 0.06 meq./g, a catalyst and water, with a polyisocyanate compound, wherein the polyurethane foam has a density of a formed article of 0.2 to 1.0 g/cm3 and C hardness of 35 to 90. However, this document does not suggest a process for improving dimensional stability with advancement of lighter weight at all.
An object of the present invention is to provide a foamed article having sufficient strength, and simultaneously satisfying soft and excellent feel and low rebound resilience.
Another object of the present invention is to provide a polyurethane foam made of a polyether-based polyurethane, which has sufficient strength even at low density and is excellent in dimensional stability, and to provide a shoe sole and a shoe having the shoe sole as applications which make good use of the features of the polyurethane foam.
These and other objects of the present invention will be apparent from the following description.